In recent years, imaging devices such as CMOSs and CCDs have become smaller in size and larger in the number of pixels, and imaging machines including such imaging devices have also become smaller in size. In this trend, imaging lenses to be mounted on these kinds of imaging machines are expected to have excellent optical performance while being small in size. Particularly, on-vehicle and surveillance cameras are expected to be small in size, have high performance, be inexpensive, and have a wide angle, and furthermore, emphasis tends to be put on high environment resistance for outdoor use.
Patent Literatures 1 and 2 disclose wide-angle imaging lenses that have power arrangement starting from negative, negative, and positive in this order from the object side, and these wide-angle imaging lenses are suggested as imaging lenses to be mounted on on-vehicle cameras. Patent Literature 1 suggests optimizing the joining surfaces of the last group, to obtain an imaging lens that is easy to manufacture and has high performance. However, such an imaging lens is hardly small enough for a sensor, and no environment resistance is taken into account. Patent Literature 2 also discloses a structure in which an elastic member is provided on the back surface of the first lens, with environment resistance being taken into account. In such a structure, however, load is applied to the first lens in the optical axis direction. As a result, the lens is lifted up, and performance such as the angle of view might vary. Although Patent Literature 2 discloses no numerical examples concerning optical shapes, it can be seen from the drawings that the total length relative to the sensor size is long, and the diameter relative to the sensor size is also long.